Absolutely convex

A set C in a real or complex vector space is said to be absolutely convex or disked if it is convex and balanced (circled), in which case it is called a disk.

A set ${\displaystyle C}$ is absolutely convex if and only if for any points ${\displaystyle x_{1},\,x_{2}}$ in ${\displaystyle C}$ and any numbers ${\displaystyle \lambda _{1},\,\lambda _{2}}$ satisfying ${\displaystyle |\lambda _{1}|+|\lambda _{2}|\leq 1}$ the sum ${\displaystyle \lambda _{1}x_{1}+\lambda _{2}x_{2}}$ belongs to ${\displaystyle C}$.

...
Wikipedia